converting dates to and from fractional julian dates are *sometimes* off by a second...

I'm dealing with an application that stores dates as fractional julian dates, eg "2456037.426632" for "2012-04-19 10:14:21"

Since Oracle only works with integer Julian dates, I"ve developed a pair of functions to convert back and forth:

CREATE OR REPLACE FUNCTION "CALENDAR3"."DATE_TO_FRACTJULIAN"

(date_in IN DATE) return NUMBER is Fjdate number;

begin

select round((to_number((to_char(date_in, 'J')),'9999999') + to_number((to_char(date_in,'SSSSS')),'99999')/86400),6) into Fjdate from dual;

return (Fjdate);

end;

and 

CREATE OR REPLACE FUNCTION "CALENDAR3"."FRACTJULIAN_TO_DATE"

(fjdate_in IN NUMBER) return DATE is Fj2date date;